Mongoid duping embedded document doesn't clear metadata

recreation.rb

class Address
  include Mongoid::Document

  field :line1, type: String
  field :line2, type: String
  field :city,  type: String
  embedded_in :addressable, polymorphic: true
end

class Person
  include Mongoid::Document

  field :name, type: String
  embeds_one :address, as: :addressable
end

class Company
  include Mongoid::Document

  field :name, type: String
  embeds_many :addresses, as: :addressable
end

p = Person.new(name: "Rubish")
p.build_address(line1: "#113", line2: "Park Plaza", city: "New York")
p.save

c = Company.create(name: "Rubish's Company")
a = p.address.dup
c.addresses << a
# MONGODB (0ms) alma_connect['companies'].update(
#    {"_id"=>BSON::ObjectId('514758c175f38e76ce000013')}, 
#    {"$set"=>{"address"=>{"line1"=>"#113", "line2"=>"Park Plaza", "city"=>"New York", "_id"=>BSON::ObjectId('514758c175f38e76ce000014'), "updated_at"=>2013-03-18 18:11:13 UTC, "created_at"=>2013-03-18 18:11:13 UTC}}})

c.reload.addresses #=> [], should have been an array with one address
c['address'] #=> actually the address I was expecting to be in addresses


# reason?
a.metadata #=> metadata from old address embedded in person
Address.new.metadata #=> nil